[ 3.5.y.z extended stable ] Patch "xen/events: fix RCU warning, or Call idle notifier after" has been added to staging queue

[Herton Ronaldo Krzesinski]

This is a note to let you know that I have just added a patch titled

    xen/events: fix RCU warning, or Call idle notifier after

to the linux-3.5.y-queue branch of the 3.5.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.5.y-queue

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From 06848989ab3961fb5970078e7b147b7cb6850c10 Mon Sep 17 00:00:00 2001
From: Mojiong Qiu <qiumojiong at gmail.com>
Date: Tue, 6 Nov 2012 16:08:15 +0800
Subject: [PATCH] xen/events: fix RCU warning, or Call idle notifier after
 irq_enter()
X-Extended-Stable: 3.5

commit 772aebcefeff310f80e32b874988af0076cb799d upstream.

exit_idle() should be called after irq_enter(), otherwise it throws:

[ INFO: suspicious RCU usage. ]
3.6.5 #1 Not tainted
-------------------------------
include/linux/rcupdate.h:725 rcu_read_lock() used illegally while idle!

other info that might help us debug this:

RCU used illegally from idle CPU!
rcu_scheduler_active = 1, debug_locks = 1
RCU used illegally from extended quiescent state!
1 lock held by swapper/0/0:
 #0:  (rcu_read_lock){......}, at: [<ffffffff810e9fe0>] __atomic_notifier_call_chain+0x0/0x140

stack backtrace:
Pid: 0, comm: swapper/0 Not tainted 3.6.5 #1
Call Trace:
 <IRQ>  [<ffffffff811259a2>] lockdep_rcu_suspicious+0xe2/0x130
 [<ffffffff810ea10c>] __atomic_notifier_call_chain+0x12c/0x140
 [<ffffffff810e9fe0>] ? atomic_notifier_chain_unregister+0x90/0x90
 [<ffffffff811216cd>] ? trace_hardirqs_off+0xd/0x10
 [<ffffffff810ea136>] atomic_notifier_call_chain+0x16/0x20
 [<ffffffff810777c3>] exit_idle+0x43/0x50
 [<ffffffff81568865>] xen_evtchn_do_upcall+0x25/0x50
 [<ffffffff81aa690e>] xen_do_hypervisor_callback+0x1e/0x30
 <EOI>  [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
 [<ffffffff810013aa>] ? hypercall_page+0x3aa/0x1000
 [<ffffffff81061540>] ? xen_safe_halt+0x10/0x20
 [<ffffffff81075cfa>] ? default_idle+0xba/0x570
 [<ffffffff810778af>] ? cpu_idle+0xdf/0x140
 [<ffffffff81a4d881>] ? rest_init+0x135/0x144
 [<ffffffff81a4d74c>] ? csum_partial_copy_generic+0x16c/0x16c
 [<ffffffff82520c45>] ? start_kernel+0x3db/0x3e8
 [<ffffffff8252066a>] ? repair_env_string+0x5a/0x5a
 [<ffffffff82520356>] ? x86_64_start_reservations+0x131/0x135
 [<ffffffff82524aca>] ? xen_start_kernel+0x465/0x46

Git commit 98ad1cc14a5c4fd658f9d72c6ba5c86dfd3ce0d5
Author: Frederic Weisbecker <fweisbec at gmail.com>
Date:   Fri Oct 7 18:22:09 2011 +0200

    x86: Call idle notifier after irq_enter()

did this, but it missed the Xen code.

Signed-off-by: Mojiong Qiu <mjqiu at tencent.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk at oracle.com>
[ herton: rediff for 3.5, no ifdef around exit_idle() ]
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 drivers/xen/events.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/xen/events.c b/drivers/xen/events.c
index 7595581..99c5345 100644
--- a/drivers/xen/events.c
+++ b/drivers/xen/events.c
@@ -1374,8 +1374,8 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs = set_irq_regs(regs);

-	exit_idle();
 	irq_enter();
+	exit_idle();

 	__xen_evtchn_do_upcall();

--
1.7.9.5